The present invention relates to a line print means suitable for a printing unit of an electrophotographic copier which scans the whole width of the maximum print size and, more particularly, to an image printing device capable of high speed processing when a plural number of smaller size images relative to the maximum print size are to be printed.
As well known in the art, in an electrophotographic copier, for example, a two-dimensional image is formed on a drum, with a photoconductive layer coated thereon, by first scanning linearly in the axis direction thereof, namely in the width direction, and then by rotating the drum before the next scan so as to move the scanning position in the length direction. Such a device is usually called as a line printer. In an electrophotographic laser printer, the printing speed does not change even when the printing width becomes narrower, because it always scans across the whole width of the maximum print size. Particularly in a printer with a laser charge-dissipater, wherein the laser beam is scanned in the width direction of the drum by a rotating polygonal mirror, the rotating rate of the drum, the scanning speed of the laser beam and the scanning width of the laser beam are all difficult to change. Accordingly, the printing speed does not increase even with narrower printing width.
Recently, a line printer of larger format is becoming popular, in which a photoconductive drum and a writing means both of larger width enable a large print like an A0 (46.8.times.33.1 inches) or E size drawing. Such a large machine was usually used for the preparation of the originals of large engineering drawings, but in view of the recent progress of CAD (computer aided design) devices, there is a need in a single printer that can print various sizes of image at a very high speed. However, when a smaller size print is processed in a line printer of larger format, the print speed remains unchanged and it takes a time corresponding to the desired number of prints.